1. Field of the Invention
The present invention relates to an exposure method and a memory medium storing a computer program.
2. Description of the Related Art
In the process of manufacturing a semiconductor device, exposure processing by an exposure apparatus is critical in determining the line width of the circuit pattern of the semiconductor device. In the exposure processing, an original is illuminated with light from a light source by an illumination optical system to project the pattern of the original onto a photoresist on a substrate via a projection optical system, thereby exposing the photoresist.
Along with the recent decrease in the circuit line width, an exposure apparatus which incorporates techniques for attaining a high resolution has been developed. Parameters which determine the resolution are the wavelength of the light source, the numerical aperture (NA) of the projection optical system, and a numeric value associated with the process (the so-called process factor K1). To attain a high resolution, there are techniques of increasing the NA and of reducing the process factor K1. Examples of the technique of reducing the process factor are modified illumination, polarized illumination, and aberration adjustment of the projection optical system.
Current techniques for attaining a high resolution have become diversified and complicated. Under the circumstances, to transfer a pattern onto a substrate with high accuracy, various parameters associated with these techniques are to be determined. Examples of these parameters are the light intensity distribution (to be referred to as the effective light source distribution hereinafter) on the pupil plane of the illumination optical system, the NA and aberration of the projection optical system, and the polarization state of the illumination light.
In the process of manufacturing a semiconductor device, one factor for the strictest precision in order to determine the yield of the device is dimensional accuracy. Dimensional accuracy is increasingly becoming higher along with a decrease in the pattern line width. This has led to a growing need to optimize various kinds of exposure conditions so as to increase dimensional accuracy to a line width value or less.
Japanese Patent Laid-Open No. 2004-247737 relates to a method of optimizing the effective light source shape. More specifically, this patent reference describes a method of optimizing an effective light source by dividing the effective light source into point sources conforming to a grating pattern and evaluating the divided point sources. This patent reference also describes a method of evaluating the critical dimension (CD), the depth of focus (DOF), the exposure allowance (EL), the depth of focus in an exposure allowance of 8% (DOF@8%EL), the dose-to-size ratio (E1:1), a dense/isolated shape bias, and an arbitrary bias attributed to the shape size. This patent reference also describes a method of evaluating side-lobe transfer, a film loss, the sidewall angle, a mask error enhancement factor (MEEF), the linear resolution, and the absolute resolution.
In the optimization of various parameters, determining the exposure condition while changing the values of individual parameters across the whole range of figures expected to be taken using these values may take a very large amount of time.